U.S. labor strikes last year rose to the highest level since 2001, with lost work days led by General Motors Co. and Chicago Public Schools.

Total work stoppages involving 1,000 or more workers climbed to 25 in 2019, with most of them education and health workers across the country, according to a Bureau of Labor Statistics report released Tuesday.

The number of strike participants fell from the prior year, but days lost topped 3.2 million -- the most since 2004. More than one-third of that total came from autoworkers at GM, whose six-week strike last year was the longest automotive walkout in half a century.

Unions have been losing members for decades, with the latest BLS data showing their ranks fell slightly to 10.3% in 2019 from 10.5% the prior year. In 1983, one-fifth of workers were represented by organized labor.

Overall, the labor market remains tight and employers desperate for skilled workers, giving workers more bargaining power. Strike activity, though, is far below levels in the mid-late 20th century. In 1981, for example, there were 145 major strikes that cost employers about 17 million working days. Levels haven’t topped 100 strikes a year since then.

One strike from last year, United Steelworkers working for Asarco in Arizona and Texas, is ongoing, according to BLS.